This invention relates to electromagnetically actuable devices and, more particularly, to electromagnet armature and pole face contact surfaces.
A conventional electromagnetically actuable device has a magnetic core proximate an armature. A coil is selectively energized to draw the armature to the magnetic core. The device may be a solenoid, a contactor, a motor starter, or the like. The armature is operatively associated with a movable device such as movable contacts or an actuator. In many instances the coil is selectively energized from an AC power source. With AC-operated electromagnets, elimination or control of noise is a prime concern. To minimize noise the surface interface of the magnetic core and armature of each device must be matched to provide minimal magnetic xe2x80x9cair gapxe2x80x9d and a stable interface surface. The minimal air gap assures sufficient force to prevent movement and the stable surface interface prevents movements due to the widely changing forces in the AC-operated device. In most conventionally devices, spring loads provide a steady force between the magnetic core and the armature. Energization of the coil counteracts the spring force to draw the armature toward the magnetic core. However, with an AC power source operating at, for example, 60 Hz, there are 120 zero crossings each second during energization. This in combination with other variations in contact surfaces can produce a noisy device.
A conventional approach to minimizing noise has been to grind all interfacing magnetic surfaces. This is a costly operation which must be done within tight limits and can have poor results. Small warping of either magnetic part can still result in an unstable and thus noisy electromagnet.
In accordance with the invention, an electromagnetically actuable device includes a formed interface to minimize noise.
Broadly, there is disclosed herein an electromagnetically actuable device having a magnetic core proximate an armature and a coil selectively energized to draw the armature to the magnetic core. The device comprises the armature, magnetic core and a formed interface there between that is adapted to provide three contact areas in a triangular configuration to provide minimal magnetic air gap and a stable interface when the coil is energized.
In one aspect of the invention the shape of the formed interface is concave.
In another aspect of the invention the shape of the formed interface is convex.
In all aspects of the invention the shape of the formed interface positioned between the armature and magnetic core provides a three point interface to minimize the magnetic air gap cause by surface deformations of the armature and magnetic core. The result is reduced vibration and noise.
It is a feature of the invention that the formed interface is formed of steel. The steel can be laminated magnetic steel. The formed interface is shaped with an arc or other shape to provide three contact areas between the magnetic core and the armature.
In accordance with one embodiment of the invention, the three contact areas can be rounded.
In accordance with another embodiment of the invention the three contact areas can be generally pointed. It will be appreciated that the three contact areas may be of an alternative shape.
It is a feature of an embodiment of the invention that a surface offset of an end portion of a formed interface is 0.002 inches or less. The surface offset promoting a minimal magnetic air gap and stable interface when the coil is energized.
It is still another feature of an embodiment of the invention that a surface offset of the end portion of the formed interface is greater than 0.002 inches. The surface offset promoting a minimal magnetic air gap and stable interface when the coil is energized.
There is disclosed in accordance with a further aspect of the invention an electromagnetically actuable device including a base. A magnetic core is fixedly mounted to the base. An armature is movably mounted to the base proximate the magnetic core. A coil is fixedly mounted to the base and is selectively energized to draw the armature to the magnetic core. A formed interface positioned between the armature and magnetic core includes mating surfaces adapted to provide three contact areas in a triangular configuration to provide minimal magnetic air gap and a stable interface when the coil is energized.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.